Wide angle mechanical stop for rotatable shafts in potentiometers and the like



Jan. 2, 1962 A. w. FRASER ETAL 3,015,793

WIDE ANGLE MECHANICAL STOP FOR ROTATABLE SHAFTS IN POTENTIOMETERS AND THE LIKE Filed April 19, 1960 FIG.\ w

INVENTORS ALTON W. FRASER JOHN F? THO/WAS m, 47% WM ATTORNEYS 3,tll5,793

WIDE ANGLE MEHANT CAL STOP FOR ROTAT- AlilLE HAFTS EN POTENTIOMETERS AND THE LIKE Alton W. Fraser, Van Nuys, and John P. Thomas,

Thousand Oaks, (Iaiifi, assignors to Technology instrurnent Corporation of Acton, a corporation of Massachusetts Filed Apr. l 1968, der. No. 23,214

6 Qlaims. (Cl. 338-l62) This invention relates to mechanical stops for rotatable shafts and more particularly to a mechanical stop asembly which permits shaft rotations in excess of 360 degrees.

As is well known, it is often necessary to provide mechanical stops for limiting rotation of an operating shaft in such diverse mechanisms as otentiometers, rotary switches, and the like. Various types of stop mechanisms have been designed, ranging from a simple stop pin which is engaged by a radial arm on the shaft whose rotation is to be limited, to more complicated mechanisms which include several cooperating elements whose configuration and disposition is critical and which necessarily occupy an excessive amount of space.

The primary object of the present invention is to provide a new and improved stop mechanism which allows shaft rotations in excess of 360 degrees and which occupies comparatively little space.

A further object of the present invention is to provide a stop mechanism assembly which can be used in connection with a variety of operating mechanisms, such as potentiometers, rotary switches, and the like.

Still another specific object of the present invention is to provide a stop mechanism in module form which can be ganged in series with a plurality of different elements having a common operating shaft whose rotation is to be limited to 360 degrees or better.

Other objects and many of the specific advantages of the present invention will become readily apparent as reference is had to the following detailed specification when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional View of a unitized package comprising a standard form of potentiometer module and a mechanical stop module embodying the present invention;

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FiG. 2 is an exploded view of the mechanical stop A module embodied in the construction of FIG. 1; and

FIG. 3 is an end view looking from right to left of the assembly of FIG. 2.

Referring now to FIG. 1, there is shown a unitized package comprising a potentiometer module A and a mechanical stop module B. The rotary potentiometer module A is of conventional construction. In this case, it is a small trimmer potentiometer which comprises a cylindrical housing 2 formed of suitable insulating material and including an end wall 4 in which is mounted a bushing 6 which rotatably supports an operating shaft 8. Since the potentiometer is a trimmer potentiometer, the shaft 8 is provided with a kerf it) for insertion of a screwdriver bit for adjustment of the potentiometer setting. Mounted within the housing 2 is a conventional resistance element generally identified by numeral 12. This resistance element comprises a card 14 on which is wound a resistance wire 16. The resistance element 12 is adhesively secured to the inside surface of the housing 2. The housing also includes three terminals 2th (only one is shown in FIG. 1). Two of the terminals 2% are connected to the resistance element adjacent the opposite ends of the wire 16. The third terminal 29 is connected to a conductive member 22 which is mounted on the bushing o within the housing 2.

Patented Jan. 2., 1%62 The operating shaft 8 of the potentiometer is provided with a split rotor at which includes a pair or" arms 28 and 259 which are forced together by means of a screw 32, thereby anchoring the rotor to the shaft 8. At a point diametrically opposed to the arms 28 and 3ft, the rotor 26 is provided with a pair of resilient contact brushes 36 which ride against the resistance element 12. The signal picked off of the resistance element by the brushes 36 is transferred to the conductive member 22 by means of a horse shoe-shaped takeoff member 4t) which is secured to the rotor 26 and which has at its ends a pair of contacts 42. and 44 which ride on the conductive element 2?).

it is to be noted that the invention is not limited to a rotary potentiometer of the type immediately described. The rotary potentiometer may be of some other suitable construction. in fact, as will more readily be apparent from the following description, the present invention may be used with some other device having a rotary operating shaft, as, for example, a commutator-type switch.

The mechanical stop module B includes a housing 50 which is formed of suitable insulating material, preferably of the same material as the housing 2 of the potentiometer module A. The housing 56 is provided with a peripheral flange 52 having a lip 54 that fits in a suitable groove formed in a flange 56 which is provided on the adjacent end of potentiometer housing 2. Flanges 52 and 5d cooperate with a split clamp ring 6% of standard construction to hold the two housings 2 and St) in tight engagement with each other whereby they will not rotate or separate relative to each other.

Housing dill is provided with an end wall 62. The interior of housing 50 is of stepped construction, including a first relatively large bore 66 immediately adjacent to the housing 2, a second smaller bore 68 communicating with the bore 66, and a third still smaller bore 70 which communicates with bore 68. The junction of bores 68 and '70 forms a shoulder 74 which acts as an end stop for a ball bearing 7'6. One race of the ball bearing is in engagement with the wall defining bore 68 and shoulder 7 and the other race of the ball bearing is secured to a stub shaft 36 which forms part of the mechanical stop module B. Stub shaft is provided with a tongue 34 (see FIG. 2) which fits in a cooperating groove as formed in the adjacent end of operating shaft 8 of the potentiometer module. Tongue 84 and groove as effectively lock shafts 8 and 8t! together so that one will rotate with the other.

Mounted on shaft 8t immediately adjacent the inner race of ball bearing 62 is a shim 90. Also mounted on shaft 8t} immediately adjacent to the shim is a disk 94,. As seen in FIG. 2, disk 94 has a central bore 96 which communicates with a radial slot 98 having the general shape of a truncated sector. The central bore 96 is sufficiently large to allow the disk to rotate freely on shaft 80. The latter has a radial pin 1% mounted thereon and projecting into the sector-shaped slot 98. The diameter of pin 100 is approximately one-half (or any other suitable dimension) of the minimum width of slot 98. Obviously, the minimum width of slot 98 is the width where it meets the central bore 96. The disk 94 is retained against the shim 90 by means of a shim file (see FIG. 1) and a retaining ring 106. Shim 104 is omitted from FIG. 2 for convenience of illustration.

The disk 94 is provided at its periphery with a radial arm 110. The outer end of radial arm is spaced from the inner surface defining bore 66 so as to allow the disk to rotate freely within the housing. Cooperating with radial arm 116 is a longitudinally extending pin 114 which is anchored in a suitable hole formed in the end wall of the housing. Pin 114 is located adjacent 3 the surrounding surface of bore 66 and it extends axially a distance sufiicient so that it will intercept radial arm- 110 when the disk 94 is rotated.

Operation of the wide angle stop mechanism is very simple. When shaft 80 is rotated, pin 101 will engage one side of the sector-shaped slot 98 and cause the disk 94 to rotate within the housing until its arm 110 strikes pin 114. At that point, disk 94 will be able to rotate no further and shaft 30 will be stopped. However, shaft 80 may be rotated in the opposite direction. As soon as shaft 80 has begun to turn in the opposite direction, pin 100 will begin to move Within the confines of the slot 98, but disk 94 will not move until pin ltltl has moved from one side to the other of slot 98. As soon as the pin 100 has traversed slot 98, disk 94 will begin to rotate again. It will continue to rotate until its arm 110 again reengages pin 14. At that point, both disk 94 and shaft 80 will be stopped again.

In view of the play between shaft 80 and disk 94 which is provided by the sector-shaped slot 98 and the pin 100, shaft 80 can be made to rotate to an angle larger than 360 degrees even though the disk 94 is able to rotate through an angle less than 360 degrees. The exact angle through which disk 94 can rotate is determined by the outside diameter of pin 114 and the width of the arm 110. The wider the arm 110 and the greater the outside diameter of pin 114, the smaller the angle through which disk 94 can rotate. The degree of rotation of shaft 80 is the sum of the maximum angle of rotation of disk 94 and the angular play provided by the sector- 'shaped slot 98 with respect to the pin 100. The object is to allow sufiicient play between pin 100 and slot 98 so as to make up for the amount of rotation of disk 94 which is eliminated or prevented by virtue of the outside diameter of pin 114 and the width of arm lllltl. In the illustrated embodiment, shaft 80 will be able to rotate through an angle slightly larger than 360 degrees. By Widening slot 98, shaft 80 can be made to rotate through a still greater angle. Conversely, by narrowing slot 98, shaft 80 can be limited to an angle less than 360 degrees. I Although the illustrated embodiment involves a stub shaft 80 which is totally confined within the housing Stl, it is to be understood that shaft 80 may be made to extend outside of housing 50 so as to be connectable to some other device. In FIG. 1, this concept of extending shaft 80 is illustrated in dotted lines at 120. Of course, when shaft 80 is extended outside of the housing '50, the end wall 62 of the housing will be provided with a suitable opening through which the shaft may extend. Similarly, the extended shaft may be provided with a kerf or slot as indicated at 122 so as to permit it to be interlocked with the operating shaft of some other device, as, for example, another potentiometer or switch. Similarly, shaft 80 need not be separate from shaft 8 of the potentiometer. If desired, shaft 8 could be made to extend fully into the housing 50 with its extension functioning as a substitute for stub shaft 80'. In the latter case, the disk 94 and the pin 100 would be mounted directly on the extension of shaft 8. This alternative form is not illustrated for the reason that its construction is sufficiently simple to comprehend without need of illustration.

The chief advantage of the foregoing invention is that it occupies very little space. In this connection, it is to be noted that potentiometer module A as illustrated is several times its normal size. In practice, trimmer potentiometers are often approximately one inch in overall diameter and up to three-quarters inches in axial length. I

with other devices such as rotary switches. As indicated above, stub shaft may be an integral part of the operating shaft of the device whose rotation is to be limited. On the other hand, it may be as is--a separate stub shaft. This versatility is advantageous since it means that stop mechanism modules B may be employed in a variety of situations with little or no change in construction.

Still another advantage of the foregoing invention is its relatively low cost. The various members embodied in the stop mechanism are inexpensive to construct and easy to assemble. Moreover, the stop mechanism need not be located directly adjacent to the device whose operating shaft is to be limited. It may be axially spaced from the device in question and may, in the case of a ganged system, be at the tail end of the gang. Thus, in a unitized gang or package comprising a rotary potentiometer, a magnetic clutch for operating the potentiometer, a spring return device for restoring the operating shaft of the potentiometer to a zero or null position, and a switch adapted to be operated when the operating shaft of the potentiometer is rotated through a predetermined angle, the illustrated stop mechanism may be located at a point removed from the potentiometer since stub shaft 80 can be interlocked to the operating shaft of the potentiometer or to any other shaft which in turn may be interlocked with the operating shaft of the potentiometer.

Obviously, many modifications and variations of the invention are possible in view of the above teachings. Therefore, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts specifically described or illustrated, and that within the scope of the appended claims, it may be practiced otherwise than as specifically described or illustrated.

We claim:

1. A wide angle mechanical stop for a shaft supported in a housing for rotation relative to said housing, comprising a first stationary pin extending parallel to said shaft but spaced therefrom a predetermined distance, a disk rotatably mounted on said shaft, means preventing said disk from moving axially along said shaft, a flat radial arm on said disk at its periphery, said arm extending radially a distance sufficient for it to engage said first pin when said disk is rotated, said disk having a radial slot, and a second pin secured directly to said shaft and extending radially into said slot, said second pin having a maximum outside diameter in said slot which is less than the minimum width of said slot, whereby when said shaft is rotated said second pin can rotate relative to said disk an amount equal to the difference between said minimum width of said slot and said maximum diameter of said pin before said disk is engaged and rotated by said second 2. In combination with a rotatable shaft, means for limiting rotation of said shaft to an angle in excess of 360 degrees, said means comprising a first radially extending pin secured to said shaft, a second longitudinally extending pin secured to a fixed element and spaced outwardly from the end of said first radial pin, and a disk mounted on said shaft, said disk having a central opening sufiiciently large to rotatably accommodate said shaft and a divergent slot communicating with said central opening, said first pin disposed in said divergent slot, said first pin having an outside diameter less than the minimum width of said slot, whereby said pin first may be rotated through a predetermined angle within the confines of said slot, and a fiat radial arm on the end of said disk extending outwardly sufficiently far to intercept said second longitudinally extending pin when said disk is rotated by said first pin.

3. In combination with a rotary potentiometer having a rotatable operating shaft, means for limiting rotation of said operating shaft to a predetermined angle substantially equal to an angle greater than 360 degrees, said means including a stub shaft interlocked with said operating shaft, a first radially extending pin aflixed to said stub shaft, a second longitudinally extending pin spaced radially from said stub shaft, means locking said second pin against movement relative to said stub shaft, and a disk rotatably mounted on said stub shaft, said disk including a slot having opposite sides which diverge outwardly from said shaft, said first pin disposed within said slot and engageable first with the one and then with the other of said opposite sides, the minimum distance between said opposite sides being substantially larger than the outside diameter of said first pin therein, whereby said first pin may be moved within said slot, and a radial arm on the peripheral edge of said disk, said radial arm extending outwardly a distance sufficient to be engaged and be blocked by said second pin when said disk is rotated by said first pin during rotation of said stub shaft.

4. The combination of claim 3 further including means preventing said disk from moving axially along said stub shaft.

5. The combination of claim 3 wherein said means holding said second pin stationary is a housing which is detachably secured to the housing of said potentiometer.

6. A mechanical stop module for attachment to a rotary potentiometer module, said mechanical stop module comprising a housing having a surrounding side wall and an end wall, said side wall having circumferentially extending means adapting said housing for attachment to the housing of a rotary potentiometer module, a shaft adapted to be coupled to the rotatable slider of said same potentiometer module, a bearing mounted in said end wall and rotatably supporting said shaft, a first radially extending pin affixed to said shaft, a second longitudinally extending pin aflixed to said end wall, a disk having a central aperture sized to rotatably accommodate such shaft, said disk also having an arcuate slot communicating with said central aperture, said shaft extending through said disk, said disk disposed adjacent to said end wall with said first pin disposed within said slot, the outside diameter of said pin being substantially less than the minimum width of said slot whereby said shaft is free to rotate a limited angular distance relative to said disk, and a fiat radial arm on the peripheral edge of said disk, said arm extending radially a distance sufficient to engage and be blocked by said second pin when said disk is rotated by said shaft, whereby a potentiometer slider coupled to said shaft will be stopped in its path of travel.

References Cited in the file of this patent UNITED STATES PATENTS 2,305,123 Williams Dec. 15, 1942 2,629,843 Berry Feb. 24, 1953 2,872,553 Hatfield Feb. 3, 1959 2,918,157 Nichols et a1. Dec. 22, 1959 

